Administration of gases and gas mixtures to patients may be required in a variety of circumstances. Where a patient has ceased breathing, or is breathing with difficulty and requires assistance, some form of resuscitation treatment by a medical assistant may be required. This may take the form of the administration of a gas mixture with or without manual assistance, or with or without a form of mouth-to-mouth resuscitation, depending upon the condition of the patient and the circumstances, and even upon the equipment available and the location. In addition, the type of resuscitation effort applied may depend upon the age of the patient. For example, infants require a more gentle form of treatment than can be applied to adults.
Another circumstance where gas administration may be required, is for analgesic purposes or for anaesthetic purposes. Where, for example, a patient is in pain, due, for example, to an injury or an accident, gas mixtures may be administered for the relief of pain. Where such a patient is involved in an accident, and is, for example, pinned by some structure or article, such gas mixtures may have to be self-administered in order to produce temporary unconsciousness so as to enable rescue workers to free the victim.
In other circumstances, a victim may be suffering from partial disability due to inhalation of noxious gases, and may simply require self-administered gas mixtures for breathing purposes in order to overcome the effects of the incident.
These are merely examples of various different situations in which the administration of gases may be required. It will be appreciated that such gases may be administered in different ways, other than those suggested herein. In addition, reference to administration of "gases" is deemed to include any gas or mixture of gases which may be administered for breathing purposes, or for any treatment of any condition, or for relief of pain, or for anaesthetic purposes, and includes the administration of fresh air.
Different problems occur when gases are administered in such a wide variety of circumstances.
For example, mouth-to-mouth resuscitation is known to produce possible undesirable results. Where direct mouth-to-mouth resuscitation is applied, simply by placing the mouth over the mouth of the patient, it is possible for the medical assistant to receive infection from the patient. Instances are well known, where, for example, paramedical personnel have become infected as a result of giving emergency mouth-to-mouth resuscitation.
In an attempt to overcome this problem, it is well known to provide some form of mouth piece and mask, by means of which mouth-to-mouth resuscitation may be given through a mask and tube. Even in this case, however, it is possible for the assistant to receive exhaled breath from the patient.
A further and more fundamental disadvantage is the fact that the medical assistant will be administering his own exhaled air. Normally, exhaled air contains approximately 15% free oxygen. This percentage is, of course, reduced in relation to normal fresh air and is generally speaking not sufficient to support life over a continuous period.
It is, therefore, highly desirable to supply some form of gas mixture or oxygen supplement when applying resuscitation.
A wide variety of different systems are available on the market for resuscitation by administering oxygen or mixtures of air and oxygen, through various forms of masks' valves and bellows-type devices or bags.
These systems do, however, involve a certain cash investment, and are often not available at the scene of the emergency. In addition, however, they do require a certain degree of training in their use. Operators of such equipment require to develop a sensitive "feel" on the pressure in the bellows or bag, so as to avoid overpressuring the lungs of the patient. If the airway is obstructed, then it is dangerous to overpressure the bag since it will increase the obstruction, and operators must be carefully trained to sense resistance.
When giving straightforward mouth-to-mouth resuscitation, however, the presence of an obstruction is more easily sensed. Resistance to air flow is immediately apparent to anyone attempting to blow into the mouth of a victim.
Accordingly, a system whereby mouth-to-mouth resuscitation could be applied, while at the same time applying supplemental free oxygen or gas mixture would be highly advantageous both from the viewpoint of initial cost and also from the viewpoint of operator sensitivity.
When gases are administered in other situations, and even self-administered, for example, for pain relief, anaesthetic purposes, or for simply recovering from smoke inhalation or the like, the existing systems currently in use provide a simple form of "demand" valve, which is connected to a pressurized source of gas. Such a demand valve incorporates an on/off valve controlling the supply of gas, and a flexible diaphragm, which senses the inhalation effort of the victim, and operates the on/off valve so that gas is supplied during inhalation. As soon as the victim exhales, the diaphragm moves in the reverse direction, and the on/off switch closes, and gas supply is halted.
Such demand valves are in wide usage.
There are, however, certain disadvantages associated with their use. If supply of the gas under pressure becomes exhausted, or if the supply tube is blocked, or bent, then the victim will be unable to breathe through the mask. If he is conscious he will, of course, immediately remove the mask. If, however, he is unconscious he may suffocate.
Demand valves of this kind may also be used for emergency administration of gases by medical personnel. Again, the assistant must be alert at all times to the possibility of blockage in the gas supply, so that he may immediately remove the mask in the event of failure.
Clearly, therefore, it is desirable to incorporate in such a demand valve an additional valving system whereby the victim or patient may be enabled to breathe atmospheric air, in the event of failure of the gas supply to the demand valve.